In commonly used screen display systems, a display screen is formed of a generally planar sheet, and the image to be displayed is projected thereon. Unfortunately, when the display is to be out of doors, the screen size requires that the holding and bracing structure be large, in turn taking up a large amount of space as well as being unsightly. Some desired applications require the screen to be mounted over a body of water such as a lake or pond, where the support of the screen becomes extremely difficult. In virtually all such applications, the screen is cumbersome and difficult to handle and orient properly.
Displays over water have their own appeal, being capable of producing a variety of novel and pleasing as well as useful effects. Among the more interesting effects is the use of a display screen created from the water itself, upon which still, or moving, colored images are projected to create the display. The projected images may constitute advertising material, signs, moving pictures, or the like, and, when the water screen is situated over a body of water, the images at night appear to be floating in the air, creating a very pleasing effect. When the visual image is accompanied by appropriate sound, the total impact on the viewer can be stunning. These effects are not readily achievable with a large, cumbersome planar screen of wood or other sheet material. The projected images are viewed from the other side of the screen than the projector side.
There have been numerous efforts and resultant apparatus directed to creating such water displays with the principal problem being the formation of the water screen itself, whether for use on land or over water. One approach entails the use of a plurality of aligned nozzles, elevated to the desired height of the screen, into which water under some pressure is pumped. The water exiting the nozzles forms a sheet of water as it falls, and this sheet forms the display screen as the water falls back into the lake or pond, or if on land, back into the water reservoir or catch basin. Such an arrangement is not totally satisfactory because the sheet of water is formed by a plurality of discrete streams, and the effect of a smooth screen surface is marred by ripples or other irregularities in the streams. In addition, it requires a pump or pumps of significant power to raise the required amount of water at the desired pressure to the elevated level of the nozzles.
In U.S. Pat. Nos. 4,974,779 and 5,067,653 of Araki et al, there are shown several embodiments of a screen forming apparatus wherein a plurality of aligned nozzles along a floating pipe have applied thereto, under pressure, an air-water mixture. The nozzles of a first group of nozzles eject pie shaped screens of the air-water mixture, and the nozzles of a second group of nozzles, interspersed between nozzles of the first group, eject fan shaped screens of the air-water mixture which overlap the pie shaped screens to form a substantially uniform smog or fog like display screen. The nozzles may be, and preferably are, arranged to eject the water upward, and the amount of water pressure supplied by the pumping mechanism determines the height of the screen, whereas the length of the array of nozzles is determinative of the width of the screen. Where large numbers of nozzles are used, which is characteristic of prior art devices as exemplified by the Araki et al patents, a great deal of pressure is required to ensure that the farthest nozzles in the array function as desired. In addition, the more nozzles that are used, the more likely it is that one or more nozzles will become clogged up or will malfunction in operation.
In virtually all prior art devices, the main emphasis is upon creating a flat, relatively smooth surfaced display screen. However, where, as is usual with display screens over water, the screen is large, a common optical phenomenon tends to degrade the picture projected onto the flat screen. When the projector itself is substantially aligned with the centerline of the screen, the center of the screen is closer to the projector than the edges of the screen are, hence the focal distance, that is, the light path, is longer for the edges of the screen than for the center thereof. Thus, where the image at the center of the screen is in focus the images at the edges are out of focus. For small screens, this effect is barely noticeable because the human eye tends to compensate to some degree. However, for large screens, the out of focus effect is too great to be ameliorated or compensated for by the observer's eye. Most efforts to overcome this inherent defect are directed to modifying the projector lens. Some success has been achieved through the use of, for example, aspheric projector lenses. Specially formulated and ground lenses, such as aspheric lenses, however, are extremely expensive, hence some other, less expensive focus compensating arrangement is much to be desired.